The invention relates to a tire having at least one component comprised of a rubber composition which contains pre-hydrophobated precipitated silica aggregates. Such tire component may be, for example although not limited to, a tire tread, sidewall and/or sidewall insert. Such pre-hydrophobated precipitated silica aggregates are contemplated as being prepared, for example, by treatment of a colloidal silica with a combination of both an organomercaptosilane and an alkylsilane.
Tires may be prepared with a rubber component which contains a precipitated silica which is hydrophobated in situ within the elastomer host by addition of both an, organomercaptosilane and an alkyl silane. For example, see U.S. Pat. No. 4,474,908.
Tires may also be prepared with a rubber component in which both an organosilyl polysulfide and an alkylsilane are individually added to a silica-containing rubber composition to treat the amorphous silica in-situ within the rubber host with both (1) a hydrophobating agent (the alkylsilane) and (2) a silica coupler (the organosilyl polysulfide compound). For example, see U.S. Pat. No. 5,780,538.
In practice, it is recognized that precipitated silica aggregates are typically hydrophilic (water attracting) in nature and, in order to aid in dispersing the silica aggregates in various rubber compositions, it is sometimes desired to make the silica aggregates more hydrophobic (water repelling) in nature and therefore more compatible with the rubber. Accordingly, and as described in the aforesaid U.S. Pat. Nos. 4,474,908 and 5,780,538, a hydrophobating agent may be added to a rubber composition in addition to the precipitated silica to combine with the silica in-situ within the rubber host to make the silica more hydrophobic in nature.
However, it is considered herein, for tire tread applications where enhanced properties such as, for abrasion resistance, are often sought, and particularly where a good homogeneous dispersion in the rubber host is often sought, that an in-situ modification of the amorphous silica within a viscous rubber host on a hit and miss basis, under relatively harsh high sheer and high temperature conditions is a relatively inefficient procedure of modifying the amorphous silica for use in rubber compositions which are intended to be silica reinforced, particularly where both an organosilane and alkyl silane are used which would compete within the rubber composition for reaction sites on the silica surface.
Accordingly, it is proposed herein to provide a tire having a component comprised of a rubber composition which contains particulate pre-hydrophobated precipitated silica aggregates where the silica aggregates are added to, or mixed with, the rubber composition in a pre-hydrophobated form instead of more inefficiently subsequently hydrophobating the silica aggregates in situ within the elastomer host.
Historically, according to U.S. Pat. Nos. 5,708,069 and 5,789,514 a silica gel may be derived by hydrophobating a silica hydrogel with both an organomercaptosilane and alkyl silane and drying the product. The resulting hydrophobated silica gel may be blended with natural rubber and/or synthetic rubber. This invention is intended to be exclusive of recovered silica gels and is intended to be limited to precipitated silica aggregates.
Also, historically, according to U.S. Pat. No. 5,750,610, an organosilicatemodified silica gel may be hydrophobated with both an organomercaptosilane and alkyl silane and the dried treated organosilicate-modified silica gel blended with natural rubber and/or synthetic rubber. This invention is intended to be exclusive of such modified silica gels.
A general description of silica gel and precipitated silica may be found, for example, in the Encyclopedia of Chemical Technology, Fourth Edition (1997), Volume 21, Kirk-Othmer, silica gel is described in Pages 1020 through 1023 as a xe2x80x9c. . . coherent, rigid, continuous three-dimensional network of spherical particles of colloidal silica.xe2x80x9d Precipitated silica is described on pages 1023 through 1026 as being xe2x80x9c. . . composed of aggregates (or secondary particles) of ultimate (or primary) particles of colloidal-size silica that have not become linked in a massive gel network during the preparation process.xe2x80x9d xe2x80x9cParticulate silica powders have a more open structure with higher pore volume than do dried pulverized gels . . . xe2x80x9d.
The pre-hydrophobated precipitated silica aggregates for this invention are intended to be exclusive of silica gels of a three dimensional network of spherical particles as referenced in the above Encyclopedia of Chemical Technology.
A further descriptive discussion of silica gels and precipitated silicas may be found, for example, in U.S. Pat. No. 5,094,829 which, as such reference, is intended to be incorporated here in its entirety.
The proposal for this invention for a tire with a component of a rubber composition which contains pre-hydrophobated precipitated silica aggregates of elementary silica particles instead of precipitated silica aggregates which are hydrophobated in situ within the elastomer host with individually added hydrophobating compounds, by treatment of a colloidal silica by both an organomercaptosilane and an alkylsilane, is considered herein to be novel and a departure from past practice.
In the description of this invention, the term xe2x80x9cphrxe2x80x9d relates to parts by weight for a material or ingredient per 100 parts by weight elastomer(s)xe2x80x9d. The terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d are used interchangeably unless otherwise indicated. The terms xe2x80x9ccurexe2x80x9d and xe2x80x9cvulcanizexe2x80x9d are used interchangeably unless otherwise indicated.
In accordance with this invention, a tire is provided which contains at least one component comprised of a rubber composition comprised of, based on 100 parts by weight (phr) of diene-based elastomer,
(A) 100 phr of at least one hydrocarbon conjugated diene-based elastomer,
(B) about 10 to about 120, alternately about 40 to about 100, phr of reinforcing filler comprised of
(i) particulate, pre-hydrophobated precipitated silica aggregates, and optionally
(ii) about 2 to about 100, alternately about 2 to about 50, phr of at least one additional reinforcing filler selected from at least one of carbon black and an additional synthetic amorphous silica, wherein said pre-hydrophobated precipitated silica aggregates are pre-hydrophobated by treating silica in anaqueous colloidal form thereof with both an organomercaptosilane and an alkylsilane in a weight ratio of said organomercaptosilane to said alkylsilane in a range of from 10/90 to 90/10;
wherein said alkylsilane is of the general Formula (I)
xe2x80x83Xnxe2x80x94Sixe2x80x94R4xe2x88x92nxe2x80x83xe2x80x83(I)
wherein R is an alkyl radical having from one to 18, preferably from one to 8, carbon atoms such as, for example, methyl, ethyl, isopropyl, n-butyl and octadecyl radicals, n is a value of from 1 to 3 and X is a radical selected from halogen, namely chlorine or bromine, preferably a chlorine radical, and alkoxy radicals, preferably an alkoxy radical as (R1O)xe2x80x94, wherein R1 is an alkyl radical having from one to 3 carbon atoms such as, for example, methyl, ethyl and isopropyl radicals, preferably from methyl and ethyl radicals, and where said organomercaptosilane is of the general formula (II):
(X)n(R2O)3xe2x88x92nxe2x80x94Sixe2x80x94R3xe2x80x94SHxe2x80x83xe2x80x83(II)
xe2x80x83wherein X is a radical selected from halogen, namely chlorine or bromine, preferably a chlorine radical, and alkyl radicals having from one to 16, preferably from one to 4, carbon atoms, preferably selected from methyl, ethyl, n-propyl and n-butyl radicals; wherein R2 is an alkyl radical having from one to 16, preferably from one to 4 carbon atoms, preferably selected from methyl and ethyl radicals and R3 is an alkylene radical having from one to 16, preferably from one to 4, carbon atoms, preferably a propylene radical; n is a value from zero to 3, preferably zero.
The hydrophobated precipitated silica aggregates might be recovered, for example, from said treated colloidal silica, for example as a treated silica hydrosol, with the aid of acid addition to the treated colloidal silica (for example, sulfuric acid or hydrochloric acid) followed by water washing and drying the recovered hydrophobated silica as a hydrophobated silica gel or as a hydrophobated precipitated silica. While this invention is not intended to be directed to a specific preparation technique (preparation of silica hydrosols, recovery of silica gels and precipitated silicas, etc.) of the pre-hydrophobated precipitated silica itself, for education purposes in this regard, reference might be made to the aforesaid Condensed Chemical Dictionary and U.S. Pat. No. 5,094,829 as well as U.S. Pat. Nos. 5,708,069, 5,789,514 and 5,750,610 for a more detailed discussion.
Representative alkylsilanes of Formula (I) are, for example, trichloro methyl silane, dichloro dimethyl silane, chloro trimethyl silane, trimethoxy methyl silane, dimethoxy dimethyl silane, methoxy trimethyl silane, trimethoxy propyl silane, trimethoxy octyl silane, trimethoxy hexadecyl silane, dimethoxy dipropyl silane, triethoxy methyl silane, triethoxy propyl silane, triethoxy octyl silane, and diethoxy dimethyl silane.
Representative organomercaptosilanes of Formula (II) are, for example, triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, and tripropoxy mercaptopropyl silane.
In further accordance with this invention, a tire of this invention is provided with said component which may be, for example, a tire tread such as for example a tread, tread cap and/or tread base; tire sidewall; tire carcass component such as for example a carcass cord ply coat; tire sidewall stiffening insert; an apex adjacent to or spaced apart from a tire bead; tire chafer; and tire bead component.
Significantly, by the practice of this invention, an addition of a coupling agent to the rubber composition for an in-situ interaction is not considered herein as being necessary for the hydrophobated silica to effectively reinforce the rubber composition because the pre-hydrophobated precipitated silica aggregates contain an integral coupling agent, namely the organomercaptosilane derived moiety.
In the practice of this invention, the various components of the tire may be a rubber composition comprised of various conjugated diene based elastomers. Such diene-based elastomers may be polymers and copolymers of conjugated dienes, such as, for example, isoprene and 1,3-butadiene, and copolymers of at least one conjugated diene hydrocarbon and vinyl aromatic compound selected from styrene and alphamethyl styrene, preferably styrene.
For example, representative of such elastomers are cis 1,4-polyisoprene rubber (natural and synthetic), cis 1,4-polybutadiene rubber, high vinyl polybutadiene rubber having a vinyl 1,2 content in a range of about 10 percent to about 90 percent, styrene/butadiene copolymer (SBR) rubber (aqueous emulsion or organic solution polymerization prepared copolymers) and including organic solvent polymerization prepared SBR having a vinyl 1,2-content in a range of about 10 to about 90 percent based on its polybutadiene derived portion and a polystyrene content in a range of about 10 to about 60 percent based upon the copolymer, styrene/isoprene/butadiene terpolymer rubber, butadiene/acrylonitrile rubber, styrene/isoprene copolymer and isoprene/butadiene copolymer rubber, 3,4-polyisoprene rubber and trans 1,4-polybutadiene rubber.
Organic solvent polymerization prepared tin coupled elastomers such as for example, tin coupled styrene/butadiene copolymers may also be used.
Tin coupled copolymers of styrene/butadiene may be prepared, for example, by introducing a tin coupling agent during the styrene/1,3-butadiene monomer copolymerization reaction in an organic solvent solution, usually at or near the end of the polymerization reaction. Such coupling of styrene/butadiene copolymers is well known to those having skill in such art.
In practice, it is usually preferred that at least 50 percent and more generally in a range of about 60 to about 85 percent of the Sn (tin) bonds in the tin coupled elastomeres are bonded to butadiene units of the styrene/butadiene copolymer to create Sn-dienyl bonds such as butadienyl bonds.
Creation of tin-dienyl bonds can be accomplished in a number of ways such as, for example, sequential addition of butadiene to the copolymerization system or use of modifiers to alter the styrene and/or butadiene reactivity ratios for the copolymerization. It is believed that such techniques, whether used with a batch or a continuous copolymerization system, is well know to those having skill in such art.
Various tin compounds, particularly organo tin compounds, may be used for the coupling of the elastomer. Representative of such compounds are, for example, alkyl tin trichloride, dialkyl tin dichloride, yielding variants of a tin coupled styrene/butadiene copolymer elastomer, although a trialkyl tin monochloride might be used which would yield simply a tin-terminated copolymer.